NEW HANGER REDUCES DRAWBACKS OF DOWNHOLE FIBER GLASS LINERS

Stephen Thorness
Baker Oil Tools
Midland, Tex.

A recently developed hydraulically operated hanger eliminates most problems with running and hanging short to medium length fiber glass liners.

The Slaughter field, a West Texas CO2 flood, illustrates the application.

SLAUGHTER FIELD

Initial development of the Slaughter field was completed in the late 1950s. The field was discovered in 1937 in Hockley and Cochran counties south of Levelland, Tex. It produces from the San Andres formation with an average depth of 4,900 ft and a pay of about 100 ft.

The field is a stratigraphic trap formed against a porosity/permeability pinchout. Secondary recovery by waterflooding started in 1959.

A CO2 miscible water-alternating-gas (WAG) injection will be used for tertiary recovery.

When fully implemented, the CO2 project area is planned to have 370 producers and 235 CO2 injectors set on a 17.7 acre "chicken-wire spacing."

CO2 injection is expected to extend the life of the field by 11 years over the expected waterflood life. Ultimate recovery should significantly increase.

Liners were needed in the Slaughter field wells to correct the following downhole problems:

Seal off a thief zone above the main pay zone. In certain areas of the field, this thief zone is in both cased and open hole completions
Seal off, in deepend wells, a high-permeability zone below the main pay. This permeable zone was squeeze cemented before running the fiber glass liner.
Repair wells with deteriorated carbon steel casing. To improve sweep efficiency of the CO2, this problem had to be corrected.
The reasons for choosing fiber glass were similar to other operators. It was determined that:
A steel liner would be short lived (possibly only 2-3 years) and the producing life of a well was planned to be extended to 15-20 years.
The cost of corrosion-resistant alloy (CRA) liner was prohibitive. Also, the option to retrieve the hanger and drill up the liner was required.
CO2 floods are very capital intensive. Economics, therefore, dictate that before redrilling a well, attempts should be made to salvage the well bore.

PREVIOUS EXPERIENCE

Other operators have set fiber glass liners on conventional steel hangers with a CRA polished-bore receptacle (PBR) underneath the hanger. The cost of an additional PBR and the lack of retrievability were disadvantages for this method.

Also, the hanger's alloy portions have limited drillability. The steel PBR and hanger would have to be milled over before reaching fiber glass.

A final disadvantage is that mechanical hangers require rotation and reciprocation during setting.

Another system used by operators involved hanging a fiber glass liner from the bottom of a permanent production packer. Again, the disadvantages are liner retrievability, need for swivel joints and other accessories rotation requirements, and cementing difficulty through a permanent packer.

FIBER GLASS

Fiber glass offers two major advantages over conventional carbon steel liners. First and foremost is its resistance to corrosion. This resistance makes fiber glass a desirable choice in CO2 injection wells. Fiber glass significantly extends the well bore's life.

Second, fiber glass is drillable, enabling the operator to remove the liner and replace it as needed. This is critical when running and cementing liners inside small diameter well bores.

A conventional repair with carbon steel liners is to hang a liner (e.g., a 4 or 3-1/2in. liner inside 5-1/2-in. casing) and as it deteriorates, attempt to repair it by squeeze cementing, hanging an even smaller liner above and through the existing liner, or abandoning the well.

A liner serves to cover and repair existing damaged casing. Therefore, repairs with steel liners are unacceptable because the new section of steel would again be exposed to the same conditions.

Fiber glass, however, also has some distinct drawbacks that had to be dealt with. These included:

Fiber glass has relatively little compressive strength. The operator of the Slaughter field chose to keep the liner out of compression by setting it off bottom.
Fiber glass has low torsional strength. The makeup torque specified for the 3-1/2in. fiber glass in this project was 375 ft/lb, and care had to be used when rotating or torquing against the fiber glass.
Fiber glass is lightweight (3-1/2-in. fiber glass is 2.8 lb/ft) and may tend to float during or after the cement job.

Although tests showed minimal damage to the fiber glass, many operators are reluctant to set conventional injection packers in it.

HANGER DESIGN

With the previous factors in mind, a liner hanger was developed that included the following:

To avoid rotating or reciprocating the liner, hydraulic action was used to set the liner.
To prevent the liner from floating, the hanger needed to hold from both directions.
To seal the liner/casing annulus, the hanger also had to function as a packer.
To allow using the hanger as the injection packer, the hanger had to have a built in polished-bore receptacle (PBR).

The hydraulic setting mechanism allows the setting tool to be on the running string and removed from the well after setting the hanger. This design accomplishes the following four objectives:

Because the body of the hanger has no pores as in conventional hydraulic set hangers, the body can be used as the PBR. This eliminates an additional PBR and allows the hanger to remain compact.
Possible leak paths are eliminated because no hydraulic chambers are needed in the hanger.
No hydraulic cylinders are in the hanger, therefore, the PBR seal inside diameter is larger.
The reusability of the setting tool reduces costs.

The setting tool must be compatible with typical liner cementing techniques, have a large enough inside diameter to let drill pipe pumpdown plugs pass, and be able to attach a shear-pinned liner wiper plug to the bottom of the setting tool.

The hanger must be retrievable so that the operator may drill up the fiber glass if desired.

Alloys and elastomers must be compatible with the CO2/WAG environment.

LINER AND HANGER

The selected hanger was originally designed for hanging slotted liners and modified to achieve the previously mentioned design factors.

The hanger is compact, and it has a large bore with a spring steel C-type bidirectional slip, a single packing element, and a shear-pin release mechanism.

The hanger has a lefthand thread in the upper bore to accept a collet latch on a seal assembly similar to that found in many permanent production packers. The hanger may be released by cutting the liner beneath the hanger and applying an upward force of approximately 30,000 lb to part the shear pins.

The fiber glass liner internal pressure rating of 2,000 psi is made from an aromatic amine cured epoxy resin with nexus veil rough coat over the area to be perforated.

The liner hanger/packer body is made from Incoloy 925, whereas, the crossover bushing between the hanger and fiber glass is made from 316 stainless steel.

A latching-type seal assembly was electroless nickel plated (ENP) externally plastic coated internally, with molyglass seals. The on/off disconnect tool was ENP internally and externally with a 316 stainless steel profile nipple and top sub.

SETTING AND CEMENTING

For the Slaughter field, a typical fiber glass liner setting and cementing procedure (Fig. 1) is as follows:

With the liner on bottom, the well is circulated bottoms up.
A freshwater pad is placed ahead of the slurry and cement is then pumped. The slurry was mixed to 16 ppg consisting of Class H cement with 10 lb/sack of an expanding additive, 4/10% dispersant, and 4/10% nonviscosifying fluid loss.
A pump down plug is placed behind the cement and displaced to the landing collar with freshwater.
To set the hanger, approximately 1,500 psi is applied through the drillstring against the liner wiper plug seated in the landing collar. This pressure moves the cone of the hanger behind the slips and packs off the packing element.
Continued pressure to about 1,800 psi will hydraulically disengage the setting tool from the hanger. The setting tool has an emergency mechanical release mechanism if the primary hydraulic function were to fail.
Care is taken in cement placement. The top of cement left slightly below the hanger avoids impairing the setting tool's retrievabihty.